no more regexp(3), so point to regex(3);

as advised by deraadt

src/lib/libc/string/bm.3

@@ -28,9 +28,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: bm.3,v 1.11 2013/06/05 03:39:23 tedu Exp $
+.\"	$OpenBSD: bm.3,v 1.12 2013/12/05 07:43:20 jmc Exp $
 .\"
-.Dd $Mdocdate: June 5 2013 $
+.Dd $Mdocdate: December 5 2013 $
 .Dt BM 3
 .Os
 .Sh NAME
@@ -100,7 +100,7 @@ The asymptotic speed of
 is
 .Pf O Ns Pq len / patlen .
 .Sh SEE ALSO
-.Xr regexp 3 ,
+.Xr regex 3 ,
 .Xr strstr 3
 .Rs
 .%R "Fast String Searching"